core_pattern: fix truncation by core_pattern handler with long parameters

We met a parameter truncated issue, consider following:
> echo "|/root/core_pattern_pipe_test %p /usr/libexec/blah-blah-blah \
%s %c %p %u %g 11 12345678901234567890123456789012345678 %t" > \
/proc/sys/kernel/core_pattern

This is okay because the strings is less than CORENAME_MAX_SIZE.  "cat
/proc/sys/kernel/core_pattern" shows the whole string.  but after we run
core_pattern_pipe_test in man page, we found last parameter was truncated
like below:

        argc[10]=<12807486>

The root cause is core_pattern allows % specifiers, which need to be
replaced during parse time, but the replace may expand the strings to
larger than CORENAME_MAX_SIZE.  So if the last parameter is % specifiers,
the replace code is using snprintf(out_ptr, out_end - out_ptr, ...), this
will write out of corename array.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 95 insertions, 60 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 9722909c4d88..ca01d2d0a6d4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -66,6 +66,12 @@ char core_pattern[CORENAME_MAX_SIZE] = "core";
 unsigned int core_pipe_limit;
 int suid_dumpable = 0;
 
+struct core_name {
+        char *corename;
+        int used, size;
+};
+static atomic_t call_count = ATOMIC_INIT(1);
+
 /* The maximal length of core_pattern is also specified in sysctl.c */
 
 static LIST_HEAD(formats);
@@ -1459,127 +1465,148 @@ void set_binfmt(struct linux_binfmt *new)
 
 EXPORT_SYMBOL(set_binfmt);
 
+static int expand_corename(struct core_name *cn)
+{
+        char *old_corename = cn->corename;
+
+        cn->size = CORENAME_MAX_SIZE * atomic_inc_return(&call_count);
+        cn->corename = krealloc(old_corename, cn->size, GFP_KERNEL);
+
+        if (!cn->corename) {
+                kfree(old_corename);
+                return -ENOMEM;
+        }
+
+        return 0;
+}
+
+static int cn_printf(struct core_name *cn, const char *fmt, ...)
+{
+        char *cur;
+        int need;
+        int ret;
+        va_list arg;
+
+        va_start(arg, fmt);
+        need = vsnprintf(NULL, 0, fmt, arg);
+        va_end(arg);
+
+        if (likely(need < cn->size - cn->used - 1))
+                goto out_printf;
+
+        ret = expand_corename(cn);
+        if (ret)
+                goto expand_fail;
+
+out_printf:
+        cur = cn->corename + cn->used;
+        va_start(arg, fmt);
+        vsnprintf(cur, need + 1, fmt, arg);
+        va_end(arg);
+        cn->used += need;
+        return 0;
+
+expand_fail:
+        return ret;
+}
+
 /* format_corename will inspect the pattern parameter, and output a
  * name into corename, which must have space for at least
  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
  */
-static int format_corename(char *corename, long signr)
+static int format_corename(struct core_name *cn, long signr)
 {
         const struct cred *cred = current_cred();
         const char *pat_ptr = core_pattern;
         int ispipe = (*pat_ptr == '|');
-        char *out_ptr = corename;
-        char *const out_end = corename + CORENAME_MAX_SIZE;
-        int rc;
         int pid_in_pattern = 0;
+        int err = 0;
+
+        cn->size = CORENAME_MAX_SIZE * atomic_read(&call_count);
+        cn->corename = kmalloc(cn->size, GFP_KERNEL);
+        cn->used = 0;
+
+        if (!cn->corename)
+                return -ENOMEM;
 
         /* Repeat as long as we have more pattern to process and more output
            space */
         while (*pat_ptr) {
                 if (*pat_ptr != '%') {
-                        if (out_ptr == out_end)
+                        if (*pat_ptr == 0)
                                 goto out;
-                        *out_ptr++ = *pat_ptr++;
+                        err = cn_printf(cn, "%c", *pat_ptr++);
                 } else {
                         switch (*++pat_ptr) {
+                        /* single % at the end, drop that */
                         case 0:
                                 goto out;
                         /* Double percent, output one percent */
                         case '%':
-                                if (out_ptr == out_end)
-                                        goto out;
-                                *out_ptr++ = '%';
+                                err = cn_printf(cn, "%c", '%');
                                 break;
                         /* pid */
                         case 'p':
                                 pid_in_pattern = 1;
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%d", task_tgid_vnr(current));
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%d",
+                                              task_tgid_vnr(current));
                                 break;
                         /* uid */
                         case 'u':
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%d", cred->uid);
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%d", cred->uid);
                                 break;
                         /* gid */
                         case 'g':
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%d", cred->gid);
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%d", cred->gid);
                                 break;
                         /* signal that caused the coredump */
                         case 's':
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%ld", signr);
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%ld", signr);
                                 break;
                         /* UNIX time of coredump */
                         case 't': {
                                 struct timeval tv;
                                 do_gettimeofday(&tv);
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%lu", tv.tv_sec);
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%lu", tv.tv_sec);
                                 break;
                         }
                         /* hostname */
                         case 'h':
                                 down_read(&uts_sem);
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%s", utsname()->nodename);
+                                err = cn_printf(cn, "%s",
+                                              utsname()->nodename);
                                 up_read(&uts_sem);
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
                                 break;
                         /* executable */
                         case 'e':
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%s", current->comm);
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%s", current->comm);
                                 break;
                         /* core limit size */
                         case 'c':
-                                rc = snprintf(out_ptr, out_end - out_ptr,
-                                              "%lu", rlimit(RLIMIT_CORE));
-                                if (rc > out_end - out_ptr)
-                                        goto out;
-                                out_ptr += rc;
+                                err = cn_printf(cn, "%lu",
+                                              rlimit(RLIMIT_CORE));
                                 break;
                         default:
                                 break;
                         }
                         ++pat_ptr;
                 }
+
+                if (err)
+                        return err;
         }
+
         /* Backward compatibility with core_uses_pid:
          *
          * If core_pattern does not include a %p (as is the default)
          * and core_uses_pid is set, then .%pid will be appended to
          * the filename. Do not do this for piped commands. */
         if (!ispipe && !pid_in_pattern && core_uses_pid) {
-                rc = snprintf(out_ptr, out_end - out_ptr,
-                              ".%d", task_tgid_vnr(current));
-                if (rc > out_end - out_ptr)
-                        goto out;
-                out_ptr += rc;
+                err = cn_printf(cn, ".%d", task_tgid_vnr(current));
+                if (err)
+                        return err;
         }
 out:
-        *out_ptr = 0;
         return ispipe;
 }
 
@@ -1856,7 +1883,7 @@ static int umh_pipe_setup(struct subprocess_info *info)
 void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 {
         struct core_state core_state;
-        char corename[CORENAME_MAX_SIZE + 1];
+        struct core_name cn;
         struct mm_struct *mm = current->mm;
         struct linux_binfmt * binfmt;
         const struct cred *old_cred;
@@ -1911,7 +1938,13 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
          */
         clear_thread_flag(TIF_SIGPENDING);
 
-        ispipe = format_corename(corename, signr);
+        ispipe = format_corename(&cn, signr);
+
+        if (ispipe == -ENOMEM) {
+                printk(KERN_WARNING "format_corename failed\n");
+                printk(KERN_WARNING "Aborting core\n");
+                goto fail_corename;
+        }
 
         if (ispipe) {
                 int dump_count;
@@ -1948,7 +1981,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
                         goto fail_dropcount;
                 }
 
-                helper_argv = argv_split(GFP_KERNEL, corename+1, NULL);
+                helper_argv = argv_split(GFP_KERNEL, cn.corename+1, NULL);
                 if (!helper_argv) {
                         printk(KERN_WARNING "%s failed to allocate memory\n",
                                __func__);
@@ -1961,7 +1994,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
                 argv_free(helper_argv);
                 if (retval) {
                         printk(KERN_INFO "Core dump to %s pipe failed\n",
-                               corename);
+                               cn.corename);
                         goto close_fail;
                 }
         } else {
@@ -1970,7 +2003,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
                 if (cprm.limit < binfmt->min_coredump)
                         goto fail_unlock;
 
-                cprm.file = filp_open(corename,
+                cprm.file = filp_open(cn.corename,
                                  O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
                                  0600);
                 if (IS_ERR(cprm.file))
@@ -2012,6 +2045,8 @@ fail_dropcount:
         if (ispipe)
                 atomic_dec(&core_dump_count);
 fail_unlock:
+        kfree(cn.corename);
+fail_corename:
         coredump_finish(mm);
         revert_creds(old_cred);
 fail_creds: